High copper low alloy steel sheet

Abstract

A high copper low alloy steel sheet less than 5 mm is made by preparing a molten melt producing an as-cast low alloy steel comprising by weight, 0.02 % to 0.3% carbon, 0.10% to 1.5% manganese, 0.01% to 0.5% silicon, greater than 0.01 % and less than or equal 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03 % tin, less than 0.10 % nickel, total oxygen level at least 70 ppm and usually less than 250 ppm, free oxygen content 20 to 70 ppm, the remainder iron and impurities, solidifying the melt into sheet less than 10 mm thickness in a non-oxidizing atmosphere to below 1080° C. Copper content may be between 0.2% and 2.0% by weight. The steel may have a corrosion index (I) of at least 6.0 in accordance with ASTM G101 where: I=26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 . The steel may be produced by twin roll casting, and may be less than 2 mm thickness.

1 . A high copper low alloy steel sheet made by the steps comprising:
 (a) preparing a molten melt producing an as-cast low alloy steel comprising
 (i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01% and 0.5% silicon, greater than 0.01% and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin, less than 0.10% nickel, a total oxygen level of at least 70 ppm, and a free oxygen content between 20 and 70 ppm; 
 (ii) the remainder iron and impurities resulting from melting; 
   (b) solidifying and cooling the molten melt into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C.   
     
     
         2 . The high copper low alloy steel sheet as claimed in  claim 1  wherein the corrosion index (I) is at least 6.0 where:
     I =26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 .   
     
     
         3 . The high copper low alloy steel sheet as claimed in  claim 1  wherein the total of the % by weight of copper is between 0.2 and 2.0. 
     
     
         4 . The high copper low alloy steel sheet as claimed in  claim 1  wherein the molten melt has a free oxygen content between 30 and 60 ppm. 
     
     
         5 . The high copper low alloy steel sheet as claimed in  claim 1  wherein the thickness of the sheet is less than 2 mm in thickness. 
     
     
         6 . The high copper low alloy steel sheet as claimed in  claim 1  wherein the molten melt has a total oxygen level is between 70 ppm and less than 150 ppm. 
     
     
         7 . A high copper low alloy steel sheet made by the steps comprising:
 (a) preparing a molten melt producing an as-cast low alloy steel comprising
 (i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01% and 0.5% silicon, greater than 0.01% and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin, less than 0.10% nickel, a total oxygen level is between 70 and 250 ppm, and a free oxygen content between 20 and 70 ppm; 
 (ii) the remainder iron and impurities resulting from melting; 
   (b) forming the melt into a casting pool supported on casting surfaces of a pair of cooled casting rolls having a nip therebetween;   (c) counter rotating the casting rolls to form a thin cast sheet of less than 10 mm in thickness extending downwardly from the nip; and   (d) cooling the cast sheet to below 1080° C. in a non-oxidizing atmosphere.   
     
     
         8 . The high copper low alloy steel sheet as claimed in  claim 7  wherein the corrosion index (I) is at least 6.0 where:
     I =26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 .   
     
     
         9 . The high copper low alloy steel sheet as claimed in  claim 7  wherein the total of the percent by weight of copper is between 0.2 and 2.0. 
     
     
         10 . The high copper low alloy steel sheet as claimed in  claim 7  wherein the molten melt has a free oxygen content between 30 and 60 ppm. 
     
     
         11 . The high copper low alloy steel sheet as claimed in  claim 7  wherein the thickness of the thin cast sheet is less than 2 mm in thickness. 
     
     
         12 . The high copper low alloy steel sheet as claimed in  claim 7  wherein the molten melt has a total oxygen level is between 70 and 150 ppm. 
     
     
         13 . A method of making a high copper low alloy steel sheet comprising the steps of:
 (a) preparing a molten melt producing an as-cast low alloy steel comprising
 (i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01% and 0.5% silicon, greater than 0.01% and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin, less than 0.10% nickel, a total oxygen level of at least 70 ppm, and a free oxygen content between 20 and 70 ppm; 
 (ii) the remainder iron and impurities resulting from melting; 
   (b) solidifying the molten melt into sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C.   
     
     
         14 . The method of making a high copper low alloy steel sheet as claimed in  claim 13  wherein the corrosion index (I) is at least 6.0 where:
     I =26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 .   
     
     
         15 . The method of making a high copper low alloy steel sheet as claimed in  claim 13  wherein the total of the percent by weight of copper is between 0.2 and 2.0. 
     
     
         16 . The method of making a high copper low alloy steel sheet as claimed in  claim 13  wherein molten melt has a free oxygen content between 30 and 60 ppm. 
     
     
         17 . The method of making a high copper low alloy steel sheet as claimed in  claim 13  wherein the thickness of the thin cast strip is less than 2 mm in thickness. 
     
     
         18 . The method of making high copper low alloy steel sheet as claimed in  claim 13  wherein the molten melt has a total oxygen level is between 70 and 150 ppm. 
     
     
         19 . A method of making a high copper low alloy steel sheet comprising the steps of:
 (a) preparing a molten melt producing an as-cast low alloy steel comprising
 (i) by weight, between 0.02% and 0.3% carbon, between 0.10% and 1.5% manganese, between 0.01% and 0.5% silicon, greater than 0.01% and less than or equal to 0.15% phosphorus, less than 0.05% aluminum, more than 0.20% copper, less than 0.03% tin, less than 0.10% nickel, a total oxygen level is between 70 and 250 ppm, and a free oxygen content between 20 and 70 ppm; 
 (ii) the remainder iron and impurities resulting from melting; 
   (b) forming the melt into a casting pool supported on casting surfaces of a pair of cooled casting rolls having a nip therebetween;   (c) counter rotating the casting rolls to form a thin cast sheet of less than 10 mm in thickness extending downwardly from the nip;   (d) cooling the cast sheet to below 1080° C. in a non-oxidizing atmosphere.   
     
     
         20 . The method of making a high copper low alloy steel sheet as claimed in  claim 19  wherein the corrosion index (I) is at least 6.0 where:
     I =26.01 (% Cu)+3.88 (% Ni)+1.20 (% Cr)+1.49 (% Si)+17.28 (% P)−7.29 (% Cu)(% Ni)−9.10 (% Ni)(% P)−33.39 (% Cu) 2 .   
     
     
         21 . The method of making a high copper low alloy steel sheet as claimed in  claim 19  wherein the total of the percent by weight of copper is between 0.2 and 2.0. 
     
     
         22 . The method of making a high copper low alloy steel sheet as claimed in  claim 19  wherein molten melt has a free oxygen content between 30 and 60 ppm. 
     
     
         23  The method of making a high copper low alloy steel sheet as claimed in  claim 19  wherein the thickness of the thin cast strip is less than 2 mm in thickness. 
     
     
         24 . The method of making high copper low alloy steel sheet as claimed in  claim 19  wherein the molten melt has a total oxygen level between 70 and 150 ppm.